The present invention relates to a new and improved construction of a sensor syringe or hollow tubular needle arrangement for the automatic withdrawal of a sample from a liquid contained within a vessel or the like and which automatically adjusts its position with respect to the unknown liquid surface.
If it is necessary to withdraw numerous liquid samples with consistent accuracy, or whenever access to the sample removal site is difficult, the withdrawal of the sample advantageously is carried out by an automatic mechanism. Also in those fields of application where manual sample removal would endanger the operating personnel due to radiation or chemical effects, it is absolutely necessary that the sample be withdrawn automatically.
Apart from reliability in operation there is also imposed upon a sensor syringe the requirement that the liquid samples are not altered, for instance due to electrical effects, and that the syringe itself not be impaired as to its operational integrity by the liquid sample.
With the aim of fulfilling these requirements there have been employed sensor syringes which detect the position of the surface of the liquid by virtue of changes in a measured physical parameter, and through the use of a suction device withdraw a quantity of sample at a certain immersion depth.
Thus, in French Pat. No. 7,425,840 there has been disclosed a sensor syringe which indicates the liquid surface by virtue of pressure fluctuations or changes of a gas flow. A pipe or tube extends parallel to a sample duct or channel, the opening of the tube being arranged in spaced relationship with respect to the opening of the sample duct. The pressure of the gas flowing through the tube varies upon immersion of the tube opening into the liquid. This pressure fluctuation is detected by a measuring device and predicated upon the measurement result there is controlled sample removal.
This sensor syringe and the required structural expenditure of equipment needed for the measurement, regulation and storage of the gas necessitates a rather voluminous piece of equipment which cannot be constructed to have an advantageous small dimensional design. A further drawback resides in the undesired expenditure in work needed for refilling or exchanging the gas container.
Additionally, there are already known in this technology sensor syringes or duct arrangements wherein there are employed capacitances and inductances as well as changes thereof upon immersion into the liquid sample for the purpose of controlling sample removal. Also with these techniques the desired miniaturisation of the sensor syringe cannot be accomplished, and additionally there is demanded a disadvantageous coupling of the sensor electronic system with the sensor zone.